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Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tail" in Greek), which typically have a very short projecting tail-like abdomen, usually hidden entirely under the thorax. [a] They live in all the world's oceans, in freshwater, and on land. They are generally covered with a thick exoskeleton. They generally have five ...
Horseshoe crabs primarily live at the water's bottom but they can swim if needed. In the modern day, their distribution is limited, only found along the east coasts of North America and South Asia. Horseshoe crabs are often caught for their blood, which contains Limulus amebocyte lysate, a chemical used to detect bacterial endotoxins.
The ocean floor is not all flat but has submarine ridges and deep ocean trenches known as the hadal zone. [6] For comparison, the pelagic zone is the descriptive term for the ecological region above the benthos, including the water column up to the surface. At the other end of the spectrum, benthos of the deep ocean includes the bottom levels ...
The crabs can travel up to 1.46 km (0.91 mi) in a day, and up to 4 km (2.5 mi) in total. [4] Only a few land crabs, including certain Geosesarma species, have direct development (the mother carries the eggs until they have become tiny, fully developed crabs), and these do not need access to water to breed.
The crabs go through five zoeal larval stages and one megalops stage before settling to the bottom in their first juvenile stage. [4] The free-swimming stages typically take three months to four months, [3] although in Alaska crabs may remain larvae for up to a year. [7] Sexual maturity is reached after about 12 molts or two years. [9]
Coconut crabs live alone in burrows and rock crevices, depending on the local terrain. They dig their own burrows in sand or loose soil. During the day, the animal stays hidden to reduce water loss from heat. The coconut crabs' burrows contain very fine yet strong fibres of the coconut husk which the animal uses as bedding. [43]
Macropodia rostrata use their eyes as well as other sensory organs to locate and catch prey. Spider crabs are omnivorous and most are underwater scavengers, and will eat anything from algae to mollusks and small fish. [2] Decorator crabs such as the Macropodia rostrata will use the algae covering their limbs as camouflage and an emergency food ...
King crabs are decapod crustaceans of the family Lithodidae [b] that are chiefly found in deep waters and are adapted to cold environments. [2] [3] They are composed of two subfamilies: Lithodinae, which tend to inhabit deep waters, are globally distributed, and comprise the majority of the family's species diversity; [3] [4] and Hapalogastrinae, which are endemic to the North Pacific and ...